The retinal pigment epithelium (RPE) is an integral component of the blood retinal barrier. Consequently, it helps to maintain the appropriate environment required for normal retinal activity. Although disruption of the RPE blood-retinal barrier and RPE transport have been associated with clinical disease, very little is known about the precise nature of these functions. The long term goal of this research is to fully characterize the transepithelial transport and barrier properties of the RPE so that clincal disease in human can be more completely understood and more effectively treated. The specific aims of this proposal are to use the in vitro rabbit RPE-choroid-sclera preparation developed in my laboratory: 1) to develop a model of RPE transepithelial transport in rabbits, 2) to determine the rabbit RPE barrier properties to biologically important substances, and 3) to determine the effects of retinal detachments upon RPE transepithelial transport and barrier function. Pharmacologic agents with known effects upon other transport systems will be used as probes for specific transport sites. The extracellular ionic milieu of the RPE will be manipulated to test for putative transport mechanisms and to determine the relative permeability of biologically importnat ions. Isotope flux studies will be used to determine the rate of transport of specific substances and the degree to which the RPE acts as a barrier to their free difffusion. These studies will be repeated using rabbits with retinal detachments to see if retinal detachment, an important clinical condition in humans, affects RPE transport and barrier functions.